[STRDB2000]

Hi there,

I recently found this forum and have been inspired to try and DIY my first sub, however after reading
dozens of posts and a lot searching online I'm completely lost!

I currently have a 250Watt M&K plate amp (6db boost at 30Hz apparently if thats important?) and wanted to build on a budget a sub that would be used for 70% music 30% HT, I don't really wan't alot of 'boom' but would prefer a tight sound that goes low if possible?

My problem is due to my tight budget and lack of reasonably priced drivers (shipping from overseas is to pricey) I don't have a lot of choice :crying: Box size is not too much of a concern (so long as I can fit them in the back of a small station wagon!) and I can do all the constuction myself so I have no extra cost there.

I have the chance to pick up two new cheap car woofers Infinity 1050W's http://manuals.harman.com/INF/CAR/Boxes%20and%20Parameters/1050W.pdf these are 4 Ohm each.

Would the knowledgeable minds here know if these would in any way be suitable drivers to use, or would I be better saving up and getting one decent quality 12" (two of the 1050W's are less than half the price here of a half decent 12" driver)

I planned to house the plate amp in its own enclosure separate from the subs, and had the idea of building a separate enclosure for each sub placing them in different areas in the room- they would then show an 8 Ohm load to he amp and so receive 180Watts each.

If they don't suit what TS spec's should I roughly be looking for in a good driver to suit the amp, I've read so much about spec's now that I don't know what I should look for?

Thanks

 

[Mike P.]

If you're lost then we'll draw you a map. :T

Is there a model number or a link to the M&K plate amp? With 2 4 ohm subs they would have to be wired for a 8 ohm load. 4 cu.ft tuned to 20 hz would be the best these subs would do with the amp that has 6 db of boost at 30 hz. I'm assuming the amp has a rumble filter at around 18 hz.

 

[ridecolby]

I may be mistaken as I am kind of new to this but if you are giving the amp a 8ohm load to get 180 watts rms do you not divide that by 2 to give 90 watts to each of the 12"s or do they actually both see 180 watts?

 

[Mike P.]

The amp is 250 watts into a 4 ohm load so both subs wired for 8 ohms will see 125 watts.

 

[ridecolby]

Not to dipute your reply Mike P. but that doesn't sound right to me. If you hook up 1 8ohm sub to that amp it sees an 8 ohm load and will put out 180w rms. so if you give it 2 4ohm subs in parrallel it sees 8 ohms and should still put out 180w correct? So if that is the case then don't the subs each get 90w?

 

[Mike P.]

Let me clarify, the amp is 250 watts into a 4 ohm load so both subs wired for 8 ohms will see 125 watts, 62.5 watts each.

 

[ridecolby]

That is more along the lines of what I thought. That makes more sense. Is that enough power to really drive these speakers? Or would he be better off driving 1 at 250w instead of feeding 2 of them such a small amount of power?

 

[Mike P.]

In the model above the input power the subs see along with the 6 db of boost put the subs at Xmax so this is the best he can do with this setup. Whether that's enough low end output will depend on what he wants.

 

[dyohn]

Not to dipute your reply Mike P. but that doesn't sound right to me. If you hook up 1 8ohm sub to that amp it sees an 8 ohm load and will put out 180w rms. so if you give it 2 4ohm subs in parrallel it sees 8 ohms and should still put out 180w correct? So if that is the case then don't the subs each get 90w?

Two 4-ohm speakers in parallel will result in a 2-ohm load on the amp. Two 8-ohm speakers in parallel will result in a 4-ohm load on the amp. Any two speakers of the same impedance connected in parallel will split the available output power equally.

 

[Mike P.]

He obviously meant series wiring.

 

[ridecolby]

He obviously meant series wiring.

Exactly my bad I did mean series. I've out of this for so many years now I am a little rusty.:rolleyesno:

 

[STRDB2000]

Wow, so many replies, thanks this forum is great!

Yes I planned to wire in series, according to the M&K specs it will deliver 180Watts into an 8 ohm load - will that mean each sub just recieves 90watts, or will the amp see both speakers as esentially one unit? http://www.apexjr.com/MnKAmp.htm

So I havn't played with winISD yet but the graph Mike P posted, does it look reasonable enough for what I hope to achieve?

Would there be any advantage to having both subs in the same enclosure or is it ok to stick with two separate ones? And as ridecolby suggested would it be better to just power one at 4 ohms with the full 250watts?

I'll have to check if theres a rumble filter, does this cut frequencies below a certain level to stop overexcursion?

Thanks again for all the replies everyone

 

[ridecolby]

I am not real well versed with Winisd etc but it would seem to me that power on with 250w would make more sense but then having twice the cone area may be better. I guess running the 2 at a lower power may be easier on all the gear and you won't be driving the speakers as hard or the amp. I sure someone on here will know better than me.

 

[Mike P.]

The amp will see both as a 8 ohm load. Depending on the size of your room, there should be room gain that will reinforce the low end output, good for HT. You'll have to experiment with sub placement in the room to get the best sound. One sub at 4 ohms won't handle the full 250watts, and you are correct about the rumble filter.

Both subs in one box will be the easiest to port. A slot port would be the easiest for this application.

 

[STRDB2000]

Both subs in one box will be the easiest to port. A slot port would be the easiest for this application.[/QUOTE]


Ok I've been having a play trying to learn winISD and managed to replicate your graph, how would I add in the 6db boost at 30Hz though?

Is there a reason a slot port would be easier?
When I go to the 'vents' tab and choose the square vent shape it tells me the diameter should be 10.2cm x 10.2cm, does this mean Im cutting a square hole for the port, is this what's meant by 'slot port'?

Sorry for all the questions, I'm new to all this so trying to learn, and I do appreciate all the help

 

[Mike P.]

Is there a reason a slot port would be easier?

Actually I made a mistake. Since the subs will be wired in series for an 8 ohm load, I forgot to change the Re value from 3.5 to 7 ohms. This has the effect of lowering the port air speed to an acceptable 21 m/s with a single 4" flared port 19" long.

To add 6 db of boost click on the EQ/Filter tab, click Add, select Parametric EQ, change the Q value to 1 and click Add.